The present invention relates generally to a technique for configuring an asynchronous transfer mode (ATM) switch or set of switches and switching ATM cells, and specifically to a method and apparatus for routing ATM cells with a generic addressing scheme that operates transparently to the physical location of the source and destination.
ATM offers an advantageous transport structure for digital communications by using a high-bandwidth multiplexing scheme for packet-based transmission of messages. ATM systems communicate information using fixed-size cells of relatively short length. FIG. 1 is a diagram of one such cell. Each cell 10 contains a 5-octet label 12, also called a header, that identifies the cell and the cell's connections. A 48-octet payload 14 follows the header in the ATM cell and carries information intended for a recipient. Switching networks rely on information stored in the header of ATM cells to switch and multiplex the cells along appropriate routes.
ATM header 12 includes a virtual path identifier (VPI) and a virtual connection identifier (VCI) label, referenced collectively as 16, together with other error detection fields 15 and functions 17. VPI-VCI 16 indicates the transport connection for user information within payload 44 and other information.
A switched ATM network will include several nodes, connected together via an ATM switch. A node may comprise a circuit board having electronics for transmitting, receiving, and processing information carried within the payload of the ATM cells. The ATM switch establishes virtual connections between the nodes such that one node can communicate with another node in the ATM network only by way of the ATM switch.
An ATM switch may include a set of virtual channel switches and at least one virtual path switch. A virtual channel switch deciphers the VCI from the VPI-VCI of a received ATM cell and routes the cell locally to nodes coupled to it. A virtual path switch couples virtual channel switches together and routes the ATM cell to an appropriate virtual channel switch based on the VPI of the VPI-VCI field 16.
The VPI-VCI for an ATM cell has a maximum length of 16 bits. Using all 16 bits for the VPI-VCI permits the addressing of 2.sup.16, or 65,536, destinations, and using fewer bits decreases the number of destinations. For example, if a switched network is configured to use only 12 bits in the VPI-VCI for addressing, the network can send an ATM cell to only 2.sup.12, or 4,096, unique interface units. On the other hand, using all 16 bits of the VPI-VCI permits the addressing of more destinations but restricts the use of those bits for other purposes.
Also, the use of unique addressing locations for each possible connection in an ATM switch limits the flexibility of adding or deleting subsystems within the switch. Each replacement module within such an ATM switch must be specially configured with the unique addresses, which increases maintenance and installation efforts. In addition, replacing or adding interface units within a conventional ATM switch may require reconfiguring the entire switch with unique addresses for the interface units.
In light of the foregoing, a need exists for an addressing structure for an ATM switched network that permits using fewer than the entire VPI-VCI field for routing ATM cells, while both allowing an increased number of connections between sources and destinations and decreasing installation and maintenance requirements.